In the microelectronics industry, copper is used in many situations because it offers an excellent electrical conductivity at a fraction of the cost of noble metals such as gold and silver. For this reason, copper particles of various sizes and shapes are used in large quantities to build conductive structures incorporated in multi layer ceramic capacitors, printed circuit boards, and many other electronic devices. Various methods including atomization, pyrolysis, electrolysis, radiolysis, and reduction of copper salts in reverse micelles and solutions are available for preparing dispersed copper particles. Among these, precipitation in homogeneous solutions is the most versatile approach as it offers a broad range of solvents and a large variety of reductants, dispersants, and complexing agents. Most dispersed copper powders currently used in microelectronics have an average particle size between 0.5 and 3.0 micrometers and are prepared by precipitation techniques involving high molecular weight polymers as dispersants. As a result they contain residual organic matter that can adversely affect their processing into electronic devices.
U.S. Pat. No. 6,875,252 (Sano, et al) describes a copper powder and process for producing copper powder. A copper powder with a narrow particle size distribution forms a pseudo-fused sintered product. This process requires ammonia to give the desired effect.
In U.S. Pat. No. 6,451,433 Oba, et al, fine metal particle dispersion solutions are produced (colloidal solution with nanometer sized particles) using citrate ion and ferrous ion under an atmosphere having substantially no oxygen.
It would be desirable to manufacture copper powders that are easily dispersed, stable to oxidation and crystalline, without the presence of polymeric dispersants that could adversely affect their use in electronic devices.